Sensitivity of gage for one gas can be correlated to its sensitivity for other gases by the ratio of gas ionization cross sections. Ionization cross sections which best correlate with gage sensitivites vary according to gage type and ionization cross section energy level

Holanda, R.

English

NASA Technical Reports Server

December 1973	 B73-10409 
NASA TECH BRIEF 
Lewis Research Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service. Springfield. Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Method of Predicting Ionization-Type

Vacuum Gage Sensitivity for Various Gases 
.
Gage Type Typical Gage 
Accelerating 
Voltage, 
Va, Volts
Ionization Cross Section, 
0° 
1. Baiard - Alpert 150 0Max or G100 or 0O.67V 3	 11 (10	 - 10	 Torr) a 
2. Triode 150 0Max or 0100 or 00.67V 
(10	 - 10 - 	 Torr) 
3. High Pressure 60 0067v 
(10	 - 1 Torr) 
4. Alphatron 10,000 05000 
(10	 - io	 Torr) 
°Numerical subscripts refer to cross section energy level in volts. 
Subscript Max refers to maximum value of cross section for 
each gas. 
tAny of these three values of cross section can be used with no 
increase in the probable error of the computed gage sensitivity. 
The Problem: 
Hot-cathode ionization vacuum gases are commonly 
used for measuring pressures below 10' 3 torr. The gages 
ionize the gas in the system by bombarding it with 
electrons. Both the ionized (i+) and ionizing (i-) particles 
are collected and measured, and the pressure (P) in the 
system is related to these two currents by the formula: 
P=
\1-
where s is the sensitivity of the gage.
Gage sensitivity is a function of characteristics of the 
gage and the properties of the gas in the system. A value 
for the sensitivity'ensitivit of a gage with a particular gas can be 
determined by calibration, however, a gage must be 
separately calibrated for each different gas on which it is 
used. A means was needed for relating the sensitivity of a 
gage for other gases to that of the gas used for calibration 
in order to eliminate calibrating each gage for every gas. 
The Solution: 
It has been determined, by experimental research and 
correlation analysis, that the sensitivity of a gage for one 
gas can be correlated to its sensitivity for other gases by 
.
(Continued overleaf) 
This document was prepared under the sponsorship of the National
	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	 will be free from privately owned rights. 
https://ntrs.nasa.gov/search.jsp?R=19730000409 2020-03-17T07:27:59+00:00Z
the ratio of the gas ionization cross sections. The 
following relation could therefore be used to predict the 
sensitivity of a gage for a particular gas: 	 - 
S (particular gas)	 =	 G (particular gas) 
S (calibration gas)	 G (calibration gas) 
How It's Done: 
The ionization cross sections which best correlate with 
gage sensitivities vary according to gage type and the 
ionization cross section energy level. The table shows the 
ionization cross sections which best correlate with gage 
sensitivities for the four different types of ionization gage 
covered by the study. Shown also are the pressure ranges 
in which the gages normally operate and the typical 
accelerating voltages for the gages. With this information, 
the relative sensitivity of a particular gage for a particular 
gas can be predicted within a probable error of 10 percent 
or less. 
Notes: 
1. The following reference was used to obtain the gas 
ionization cross sections: D. Rapp, P. Englander. 
Golden: J. Chem. Phys., Vol. 43, p. 1464, 1965. 
2. Further information is available in the following 
report: 
NASA TN-D-6815 (N72 .28454), Sensitivity of 
Hot-Cathode Ionization Vacuum Gages in Several 
Gases 
Copies may be obtained at cost from: 
Aerospace Research Applications Center 
Indiana University 
400 East Seventh Street 
Bloomington, Indiana 47401 
Telephone: 812-337-7833 
Reference: B73-10409 
3. Specific technical questions may be directed to: 
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B73-10409 
Patent Status: 
NASA has decided not to apply for a patent. 
Source: Raymond Holanda
Lewis Research Center
(LEW-1 2056)
. 
. 
Category 03	 B73.10409


Method of predicting ionization-type vacuum gage sensitivity for various gases

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server